Numerous circuits are already known which utilise said principle, both in the field of radar modulators and in the field of pulse generators for supplying induction accelerators. The latter generators have in particular been developed in the USA by the Lawrence National Livermore Laboratory.
FIG. 1 diagrammatically shows a known saturable inductor pulse generator. Said generator comprises a capacitor C1, which is charged to relatively low voltage, e.g. 30 kV, and which initially contains the energy necessary for producing a pulse at the terminals of a charge or load R. Use is e.g. made of a 2.2 microfarad capacitor C1 if it is wished to obtain, at the generator output, an energy of approximately 1 kJ in the load R. A switch I, e.g. constituted by a spark gap switch, a thyristor chain or a gas thyratron, makes it possible to discharge the capacitor C1 in to a capacitor C2, via a transformer T, whose transformation ratio n generally close to 10. In order that the transfer efficiency from C1 to C2 is at a maximum, it is necessary that the capacitance of C2 is equal to that of C1, divided by n.sup.2. If n is equal to 10 and if C has a capacitance of 2.2 microfarads, a capacitor C2 with a capacitance of 22 nF will be chosen.
Said capacitor C2 is fitted between the terminals of the secondary of the transformer T. One of its terminals, designated A1 in FIG. 1, is connected to earth or ground. The other terminal of T is designated A. The voltage V.sub.A at the terminals of the capacitor C2 varies as a function of time t in accordance with the curve shown in FIG. 2, where it can be seen that in the aforementioned numerical example, a voltage of 300 kV is reached at the end of approximately 1 microsecond. A high voltage such as this in practise makes it possible to use a capacitor C2 having a high permittivity dielectric, e.g. an electrically insulating liquid such as water, whose permittivity of approximately 80 makes it possible to obtain the high capacitance required for the capacitor C2.
The generator shown in FIG. 1 also comprises a coaxial shaping line Zo, a saturable inductor L1, another saturable inductor L2 and as well as an inductor L3, whose function will be explained hereinafter. One end of the central conductor of the line Zo is connected to the terminal A via saturable inductor L1 and the other end of said central conductor is connected to a terminal of the load R via saturable inductor L2. The other terminal of the load R is connected to one end of the outer conductor of the line Zo, whilst the other end of said outer conductor is connected to the grounded terminal A1.
Throughout the charging of the capacitor C2, the discharging current transversing the saturable inductor L1 remains sufficiently low to be ignored. This inductor L1 can be constructed in such a way that it becomes saturated as soon as the maximum voltage is reached at the terminals of C2. The inductor L1 then becomes very low and the current transversing it increases considerably in such a way that the capacitor C2 discharges into the shaping line Zo. If the capacitance of the latter is identical to that of C2, the energy transfer takes place from one to the other at a constant voltage with an efficiency close to 1. In the same way as in the preceding stage, throughout the charging time of the line Zo, a discharging current appears, which passes through the saturable inductor L2 and remains low for as long as the maximum charging voltage of Zo is not reached. Inductor L2 is constructed in such a way that it is saturated at the time when said maximum voltage is reached, the line Zo discharging into the load R, which is equal to the characteristic impedance of the line Zo. Under these conditions, a square-wave pulse appears at the terminals of the load R and its duration is equal to the outward and return time of the electric pulse in the line Zo and whose amplitude is equal to half the charging voltage of said line Zo, i.e. an amplitude of e.g. 130 kV.
The inductor L3, whereof one terminal is connected to the terminal A, is used for demagnetizing the respective cores of the transformer T and the saturable inductor L1 following an electric pulse. The other terminal of L3 is supplied by a d.c. voltage of appropriate polarity, in order to ensure the demagnetization of said cores.
FIG. 3 diagrammatically shows another electric pulse generator of the saturable inductor type and which is known in the art. Said other generator differs from that shown in FIG. 1 by the fact that the single coaxial line Zo is replaced by a double coaxial line Z1, i.e. a so-called BLUMLEIN coaxial line. Said double coaxial line Z1 comprises three electrodes, namely a central electrode E2 between an external electrode E1 and an internal electrode E3. In the generator shown in FIG. 3, one end of the electrode E2 is connected to the terminal A1 across the saturable inductor L2 and the other end of said electrode E2 is connected to the terminal A across the saturable inductor L1. One terminal B of the load R is connected to one end of the internal electrode E3, whose other end is free, whilst the other terminal of the load R is connected to one end of the external electrode E1, whose other end is connected to the terminal A1.
In the generator shown in FIG. 3, switching takes place by the saturable inductor L2 which, at the time of its saturation, short-circuits the electrodes E1 and E2, so that at the terminals of the load R appears a pulse, whose corresponding voltage V.sub.B is represented as a function of the time t in FIG. 4. It is a substantially square-wave negative pulse i1, whose amplitude is equal, in absolute values, to the maximum of the charging voltage V.sub.A, which represents the interest of the generator shown in FIG. 3.
During the charging of the line Z1, approximately half the charging current passes through the load R, which produces a "prepulse" i2, which can also be seen in FIG. 4.
The saturable inductor-type electric pulse generators known in the art suffer from the disadvantages of large overall dimensions and high cost, which considerably decreases the interest therein.